Technical Abstract:
The scaling behavior of surface (0-6cm) soil moisture variability was observed in the field during the Southern Great Plains 1999 experiment (SGP99). Nested 7x7 grids were sampled within a 1,600m field at five distinct resolutions (200m, 100m, 16m, 2m, and randomly within a 2m square) on 10 dates in mid-July, 1999. In total, over 4,000 measurements of volumetric moisture content were made by over a dozen SGP99 participants i fields LW21, LW22, and two adjacent sites which are located at the headwaters of the Little Washita river on the western boundary of the watershed. This study extends previous work during SGP97 in which soil moisture variations were monitored within several 800m fields on a 7x7 100m grid. Results of the SGP99 scaling study confirm the SGP97 findings and show that soil moisture variability increases with increasing scale. Specifically, the variance of soil water content increases systematically with scale, as does the coefficient of variation vs. mean moisture content relationship. The evolution of the soil moisture distributions mimics that observed during SGP97 on grid resolutions up to 100m but deviates on the largest, 200m grid. At this scale (the entire 1,600m field), the differences between fields (e.g., in cover type) dominate within field heterogeneity and, hence, control the shape of the distribution. Results have implications for the parameterization of soil water dynamics in hydrological and land surface models, for downscaling coarser-scale remote observations, and for upscaling point measurements.